Question

我用MySQL编写了这个查询，它可以工作：

select c.*
from macchine.check_list c
join (select pratica, documentazione, max(versione) as versione
      from macchine.check_list
      group by pratica, documentazione) c2
  on c.pratica = c2.pratica
  and c.documentazione = c2.documentazione
  and c.versione = c2.versione;

然后我尝试使用JPA存储库在我的网络应用上移动此查询：

@Query("select t1 from CheckList as t1 join "
        + "(select pratica, documentazione, max(versione) as versione from CheckList group by pratica, documentazione) as t2 "
        + "on t1.pratica = t2.pratica  and "
        + "t1.documentazione = t2.documentazione and "
        + "t1.versione = t2.versione")

但是它不起作用，因为我知道，要创建一个与JPA存储库的连接，你必须做一些像：

form table1 t1 join t1.table2 t2 on etc.

但是在这种情况下我需要在同一个表上进行连接，那么我该怎么做呢？

Answer 1

我解决了添加nativeQuery = true。

所以这是我的问题：

@Query(value = "select t1.* from macchine.check_list as t1 join "
        + "(select pratica, documentazione, max(versione) as versione from macchine.check_list group by pratica, documentazione) as t2 "
        + "on t1.pratica = t2.pratica  and "
        + "t1.documentazione = t2.documentazione and "
        + "t1.versione = t2.versione where t1.pratica = :pratica", nativeQuery = true)

要明确这是我的表：

+----+----------------+---------+----------+---------+
| id | documentazione | pratica | versione | ....... |
+----+----------------+---------+----------+---------+
| 1  | 1              | 1       | 1        |         |
+----+----------------+---------+----------+---------+
| 2  | 2              | 1       | 1        |         |
+----+----------------+---------+----------+---------+
| 3  | 3              | 1       | 1        |         |
+----+----------------+---------+----------+---------+
| 4  | 1              | 1       | 2        |         |
+----+----------------+---------+----------+---------+

并使用此查询结果如下：

+----+----------------+---------+----------+---------+
| id | documentazione | pratica | versione | ....... |
+----+----------------+---------+----------+---------+
| 4  | 1              | 1       | 2        |         |
+----+----------------+---------+----------+---------+
| 2  | 2              | 1       | 1        |         |
+----+----------------+---------+----------+---------+
| 3  | 3              | 1       | 1        |         |
+----+----------------+---------+----------+---------+

Answer 2

JPA不支持JOIN内联视图。通过这种连接过滤结果的主要替代方法（在JPQL和SQL中）通过WHERE子句中的相关子查询过滤它们：

select t1
from CheckList t1
where t1.versione = (
  select max(versione)
  from CheckList t2
  where t2.pratica = t1.pratica
    and t2.documentazione = t1.documentazione
)

Answer 3

您可以在MySQL中使用子选择创建视图，然后将该视图映射到Java实体并在CheckList中添加必要的映射：

@OneToOne
@JoinColumns(
{
    @JoinColumn(name="pratica"),
    @JoinColumn(name="documentazione"),
    @JoinColumn(name="versione")
}
private MaxCheckList maxCheckList;

@Query("select t1 from CheckList as t1 join maxCheckList t2")

如何使用与JPA Repository相同的表进行连接？

3 个答案: